Method for depositing braze alloy

ABSTRACT

The present invention relates to a method for depositing braze alloy on a surface of a component that will be subsequently joined to a second component. In one form a braze alloy is sprayed by a thermal process. The braze alloy is sprayed in such a fashion that substantially all of the powder braze alloy is unmolten, but is heated to a state deformable enough to bond to the surface. One form of the spraying operation utilizes a High Velocity Oxygen Fuel spray gun.

BACKGROUND OF THE INVENTION

1. The present invention relates in general to the braze joining ofmetal components with a braze alloy. More particularly, one embodimentof the present invention relates to the thermal spraying, of a nickelbraze alloy on surfaces of metallic components that will subsequently bejoined together. While one embodiment of the present invention wasdeveloped for the manufacture of gas turbine engine components, certainapplications may be outside of this field.

2. It is generally well known that a high temperature causing thebrazing alloy to completely melt will produce on the depositing surfacea resistant oxide membrane, which renders the surface less brazeable.Thus, the resistant oxide membrane will limit the effectiveness of thebrazing agent layer to join two metal components together. In the caseof thermal spraying of the brazing agent at extremely high temperatures,a considerable amount of the brazing agent may evaporate therebycreating difficulties in achieving uniformity in coating deposition.Further, certain brazing agents contain brazing alloy that may pre-reactduring or after melt deposition on the target surface. This pre-reactionof braze alloy elements impairs the subsequent braze joining, of themetal components.

3. Methods are generally known to produce brazeable aluminum componentsusing aluminum-silicon, aluminum-zinc, and aluminum-silicon-zinc alloys.The prior methods were often multi-step processes that deposited thealloy in a molten or semi-molten state, while delivering the fluxemulsion in a separate spray. Further, the prior deposition methodsgenerally recommend spraying the brazing agent in a non-oxidizingatmosphere such as N₂ gas, and required extensive surface preparationprior to deposition. Additionally, lower spray velocities previouslyused were not very effective. When the particles struck the surface atslower speeds they tended to peel away even though they were softened bythe heating and quenched by contact with the base material surface.

4. In one particular method an aluminum-brazing agent was delivered byplasma arc spraying. A number of difficulties occurred including thatthe high temperatures associated with plasma arc spraying pre-reactedthe fluxing agent. The high temperatures causing the aluminum alloy tobe in a molten state produced on the surface a resistant oxide membrane,which renders the material less brazeable. There were also difficultiesin achieving uniformity of deposition due to evaporation of thethermally sprayed alloy at such high temperatures.

5. Prior methods of joining components together by brazing have includedplacing the braze alloy with a tape/powder/prewet technique. This methodhas a litany of limitations that include limitations on the componentgeometry, long prewet time, and surface preparation that generallyrequired grit blasting.

6. Although the prior methods of depositing braze alloys and brazejoining are steps in the right direction, the need for additionalimprovements still remains. The present invention satisfies this need ina novel and unobvious way.

SUMMARY OF THE INVENTION

7. One form of the present invention contemplates a method fordepositing a braze alloy. The method comprising: thermally spraying apowder braze alloy onto a surface. The powder braze alloy is in such astate that substantially all of the powder braze alloy is unmolten butis heated to a state deformable enough to bond to the surface.

8. Another form of the present invention contemplates a method fordepositing braze alloy, comprising: thermally spraying a powder brazealloy at a high velocity onto a surface in such a state thatsubstantially all the powder braze alloy is unmolten, but is heated to astate malleable enough to bond to the surface.

9. Another form of the present invention contemplates a method fordepositing braze alloy, comprising; flame spraying a powder braze alloyat a high velocity onto a surface. The flame spraying occurs with astoichiometrically neutral or fuel rich flame. The flame sprayingprocess is such that the powder braze alloy is in such a state thatsubstantially all the powder braze alloy is unmolten but is heated to astate malleable enough to bond to the surface.

10. One object of the present invention is to provide an improvedtechnique to apply braze alloy to components for subsequent joining.

11. Related objects and advantages of the present invention will beapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

12.FIG. 1 is an illustrative view of a gas turbine engine.

13.FIG. 2 is a perspective view of a gas turbine engine airfoil,comprising a portion of FIG. 1.

14.FIG. 3 is a diagrammatic view of one form of the present inventioncomprising a High Velocity Oxygen Fuel (HVOF) spray process.

15.FIG. 4a is a view of a braze alloy deposited by a tape/powder/preweton a surface.

16.FIG. 4b is a view of a braze alloy applied with one form of the HighVelocity Oxygen Fuel spray process of FIG. 3.

17.FIG. 5a is a view of a braze joint created with the prior arttape/powder/prewet applied braze alloy.

18.FIG. 5b is a view of a braze joint created with HVOF preplaced brazealloy.

DESCRIPTION OF THE PREFERRED EMBODIMENT

19. For the purposes of promoting an understanding of the principles ofthe invention, reference will now be made to the embodiment illustratedin the drawings and specific language will be used to describe the same.It will nevertheless be understood that no limitation of the scope ofthe invention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

20. Referring the FIGS. 1 and 2, there is illustrated a gas turbineengine 20 which includes a compressor 21, a combustor 22, and a powerturbine 23. The three components have been integrated together toproduce an aircraft flight propulsion engine. The term aircraft isgeneric and includes helicopters, airplanes, missiles, unmanned spaceddevices and any other substantially similar devices. It is important torealize that there are a multitude of ways in which the gas turbineengine components can be linked together. Additional compressors andturbines can be added with intercoolers connecting between thecompressors and reheat combustion chambers could be added between theturbines.

21. Further, the gas turbine engine is equally suited to be used for anindustrial application. Historically, there has been widespreadapplication of industrial gas turbine engines, such as pumping sets forgas and oil transmission lines, electricity generation, and navalpropulsion. A plurality of turbine blades 24 are coupled to a rotor diskthat is affixed to a shaft rotatable within the gas turbine engine 20. Aplurality of vanes 25 are conventionally joined together to collectivelyform a complete 360° nozzle. It is understood herein that gas turbineengine blades and/or vanes are often referred to as airfoils. Otherproducts utilizing the present invention are contemplated hereinincluding but not limited to combustion liners, exhaust nozzles, exhaustliners, airframe wing leading edges and/or other fabricated components.One form of the present invention allows the joining of dissimilarmetals with a braze alloy that is compatible with complimentingmetallurgical structures. An alternate form of the present inventionallows the braze joining of similar metals with a braze alloy.

22. Referring to FIG. 3, a thermal coating spraying apparatus 30 ispositioned relative to a base material 40 for delivering a coating 41 ofbraze alloy material thereon. In the preferred embodiment, the sprayingapparatus 30 is a HVOF (High Velocity Oxygen Fuel) spray gun. It is wellknown that a HVOF process is a flame spray coating deposition processthat can apply a dense, very low porosity coatings. The controlled BTUoutput and high gas velocity imparts both thermal and kinetic energy tothe powder braze alloy particles. One spraying apparatus of this type isdisclosed in U.S. Pat. No. 4,999,225 to Rotolico incorporated herein byreference, and is available from the Perkin Elmer Corporation ofNorwolk, Conn. Other HVOF spraying apparatuses of this general type areavailable in the market place and are known to those of ordinary skillin the art. In a preferred embodiment the Diamond Jet HVOF spray gun,manufactured by Sulzer Metco (US) Inc., with the DJ 2600 hybridair/water cooled air cap assembly enhancement package that produceshigher spray velocities than the standard Diamond Jet hardware isutilized. The DJ 2600 is intended for use only with hydrogen as the fuelgas to produce premium quality HVOF coatings. The DJ 2600 optionprovides the Diamond Jet spray gun with gas velocities of up to 7000ft/sec whereas gas velocities typically approach 4500 ft/sec on thestandard Diamond Jet spray gun. However, the present invention is notintended to be limited to the use of this particular spray gun. The useof other HVOF spray guns is contemplated herein.

23. The thermal spraying process associated with HVOF guns heats and/ormelts ceramic or metal stock/powder coating. The powder or stock is thenfed through the center of the HVOF gun 30 and the heated coatingmaterial is carried by the high velocity fluid stream to the surface fordeposition. In a preferred embodiment, the HVOF process delivers theheated coating material particles 45 to the base surface material 40 atsupersonic speed. Delivery of the heated coating material particles 45to the base material surface 40 at supersonic speeds creates amechanical interlock between the base surface material 40 and thesprayed coating material 41. It is preferred that the heated material bedelivered at speeds equal to Mach 2 or greater. However, in an alternateembodiment, the delivery of the coating material occurs at speeds thatare about equal to the speed of sound.

24. The high velocity of the malleable impinging particle spray 45 ontothe base material 40 produces a dense, uniform, low porosity coating 41.The braze alloy coatings applicable for base material braze joininginclude a wide variety of materials. The following coatings and basematerials, however, have been found to provide preferred results inconjunction with the HVOF conditions discussed below.

25. One preferred embodiment is the deposition of braze alloy AmdryDF-4B onto base metal AF2-1DA-6. A more preferred embodiment is thedeposition of Amdry BRB braze alloy onto base metal AF2-1DA-6. It isunderstood herein that other braze alloys such as nickel or cobaltsuperalloys may be deposited using this method as long as they arehomogenous compounds. The DF-4B braze alloy composition is: 14Cr,Bal.Ni, 10Co, 3.5Al, 2.75B, 2.5Ta, 0.02Y. The AF2-IDA-6 base metalcomposition is: 12Cr, Bal.Ni, 10Co, 2.75Mo, 6.7W, 2.8Ti, 4.6Al, 0.015B,0.0Zr, 1.5Ta. The Amdry BRB braze alloy composition is: 13.5Cr, Bal.Ni,9.5Co, 4.0Al, 2.5B, 0.1Y. With these powder braze alloys, the followingparameters were developed for the HVOF system to utilize a neutral orfuel rich flame condition to retard the pre-reaction of braze with basematerial. All flow rates have units of S.C.F.H. (standard cubic feethour). The fuel used in the Diamond Jet 2600 spray gun is H₂. Theprimary gas type is oxygen (O₂) at 175 psi and primary flow of 26S.C.F.H. Secondary gas is H₂ at 140 psi and secondary flow of 62S.C.F.H. The airflow is 46 S.C.F.H. at 20 psi. The carrier flow was ofN₂ gas at 150 psi with a carrier flow of 55 S.C.F.H. The spray powderwas fed into the gun at a rate of 5 lbs./hr. Referring to FIG. 3, thepreferred spray distance 50 is about nine inches. In another preferredembodiment, the base surface material 40 is prepared with sixty-gritsilicon carbide paper and is degreased with Acetone.

26. In an alternative embodiment the base surface material 40 ispreheated to 150 degrees Fahrenheit. This can be accomplished bydirecting the HVOF gun's flame onto the base surface material 40 topreheat it. Upon reaching the appropriate temperature for deposition ofthe selected material, the powder braze alloy is fed through the HVOFgun. It is understood that using the HVOF gun is one technique ofpreheating base surface material 40, however, other preheatingtechniques, such as preheating in an oven, are contemplated herein. Thebraze alloy used is homogenous. Both the Amdry BRB and DF-4B alloy arepreferably used with particle sizes in the range of ASTM mesh size−140+325 or −106+45 microns. The particle sizes were selected based ontheir superior resistances to melting and entraining oxides therein.Additionally, particle size affects compression during the secondarybraze operation utilized to join the metallic components together.

27. In the preferred mode the oxygen, fuel, and carrier gas pressuresand flow rates previously given result in a neutral or slightly fuelrich flame. This type of flame retards oxidation of the braze alloy bycreating a circular flame which shapes the powder stream and acceleratesthe particles to the surface.

28. In one embodiment flame velocity is about 4,000 fl/sec. and impartsboth thermal and kinetic energy to the impinging powder braze alloyparticles. In one embodiment the partical velocity being in the range ofabout 1,200-1,600 ft/sec. The particles are malleable but substantiallyunmolten. This results in mechanical adhesion to the surface. Since theadhesion is mechanical, minimal surface preparation is necessary priorto depositing the braze alloy coating. Since the particles are not in asemi-molten condition there is little loss or uneven distribution due toevaporation. In this method, the braze alloy is delivered in a singlespray stream. The environment surrounding the process can be the ambientshop floor condition and need not be a non-oxidizing or an evacuatedatmosphere.

29. Prewetting involves heating the base material and braze alloy to atemperature that causes the braze alloy to partially melt. A hightemperature and softened braze alloy result in some of melting pointsuppressants in the braze alloy diffusing into the base material. Thisresults in an increase in the braze alloy melting point, which islimited by how hot a material can be taken during brazing where thebraze alloy does not react the same due to the loss of certain elements.

30. In contrast to the tape/powder/prewet cycle, there is no substantialloss of braze alloy potential due to diffusion. This results in bothbetter braze flow and wettability as well as better joint fillingcapability. Additionally there are time and cost savings in partpreparation and vacuum furnace operation by using the HVOF sprayingprocess instead of the labor intensive tape/powder/prewet cycle. Thebraze alloy can be preplaced on contoured and complex surfaces and thebase material is not subjected to high prewet temperatures. Thermalspraying also allows for the possibility of applying braze alloy inpatterns by masking certain areas. Also, there is no concern of aresidue of an adhesive as in the tape/powder/prewet cycle.

31. With reference to FIG. 4a and 4 b, these two photographs show theadvantages of uniformity of deposition achieved by HVOF applied brazealloy powder in contrast to braze alloy powder deposited by the priorart tape/powder/prewet method. FIGS. 5a and 5 b show a braze jointcreated with the prior art tape/powder/prewet applied braze alloy andbraze joint created with HVOF preplaced braze alloy.

32. While the invention has been illustrated and described in detail inthe drawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. A method comprising: providing a powder braze alloy; and thermally spraying the powder braze alloy and onto a surface in such a state that substantially all the powder braze alloy is unmolten but is heated to a state deformable enough to bond to the surface.
 2. The method of claim 1 , wherein said spraying is a High Velocity Oxygen Fuel process, and wherein said spraying preplaces the braze alloy on the surface.
 3. The method of claim 2 , wherein the High Velocity Oxygen Fuel process utilizes H₂ as its fuel.
 4. The method of claim 3 , wherein the spray distance is about 9 inches.
 5. The method of claim 4 , which further includes roughening and degreasing the surface.
 6. The method of claim 4 , wherein the braze alloy is a nickel super alloy.
 7. The method of claim 4 , wherein the melting point suppressant is boron.
 8. The method of claim 6 , wherein the melting point suppressant is boron.
 9. The method of claim 8 , which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 10. The method of claim 9 , wherein the High Velocity Oxygen Fuel process utilizes a Diamond Jet 2600 spray gun.
 11. The method of claim 10 , wherein the spray gun utilizes a powder feed rate of about 5 pounds per hour.
 12. The method of claim 11 , wherein the flame velocity is about 4,000 ft./sec.
 13. The method of claim 1 , wherein: said spraying is a High Velocity Oxygen Fuel process utilizing H₂ as a fuel; said spraying preplaces the braze alloy on the surface; said providing includes a nickel super alloy as the braze alloy and boron as the melting point suppressant; and which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 14. The method of claim 2 , wherein the High Velocity Oxygen Fuel process utilizes a neutral flame.
 15. The method of claim 2 , wherein the High Velocity Oxygen Fuel process utilizes a fuel rich flame.
 16. The method of claim 13 , wherein the High Velocity Oxygen Fuel process utilizes a neutral flame.
 17. The method of claim 13 , wherein the High Velocity Oxygen Fuel process utilizes a fuel rich flame.
 18. A method comprising: providing a powder braze alloy; and thermally spraying the powder braze alloy at a high velocity onto a surface in such a state that substantially all the powder braze alloy is unmolten but is heated to a state malleable enough to bond to the surface.
 19. The method of claim 18 , wherein said spraying is a High Velocity Oxygen Fuel process, and wherein said spraying preplaces the braze alloy on the surface.
 20. The method of claim 19 , wherein the High Velocity Oxygen Fuel process has H₂ as its fuel.
 21. The method of claim 20 , wherein the velocity of the powder is about 1,200 ft./sec. to 1600 ft/sec.
 22. The method of claim 21 , wherein the carrier gas is N₂.
 23. The method of claim 21 , wherein the spray distance is about 9 inches.
 24. The method of claim 23 , which further includes roughening and degreasing the surface.
 25. The method of claim 23 , wherein the braze alloy is a nickel super alloy.
 26. The method of claim 23 , wherein the melting point suppressant is boron.
 27. The method of claim 25 , wherein the melting point suppressant is boron.
 28. The method of claim 26 , which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 29. The method of claim 27 , wherein the High Velocity Oxygen Fuel process utilizes a Diamond Jet 2600 spray gun.
 30. The method of claim 28 , wherein the spray gun utilizes a powder feed rate of about 5 pounds per hour.
 31. The method of claim 18 , wherein: said spraying is a High Velocity Oxygen Fuel process utilizing H₂ as a fuel; said spraying preplaces the braze alloy on the surface; said providing includes a nickel super alloy as the braze alloy; and which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 32. A method comprising: providing a powder braze alloy; and flame spraying the powder braze alloy at a high velocity onto a surface in such a state that substantially all the powder braze alloy is unmolten but is heated to a state malleable enough to bond to the surface.
 33. The method of claim 32 , wherein said flame spraying utilizes a neutral flame.
 34. The method of claim 33 , wherein said flame spraying is a High Velocity Oxygen Fuel process, and wherein said spraying preplaces the powder braze alloy on the surface.
 35. The method of claim 34 , wherein the High Velocity Oxygen Fuel process utilizes H₂ as its fuel.
 36. The method of claim 35 , wherein the flame velocity is about 4,000 ft./sec.
 37. The method of claim 36 , wherein the carrier gas is N₂.
 38. The method of claim 36 , wherein the spray distance is about 9 inches.
 39. The method of claim 38 , which further includes the steps of roughening and degreasing the surface.
 40. The method of claim 38 , wherein the braze alloy is a nickel super alloy.
 41. The method of claim 38 , wherein the melting point suppressant is boron.
 42. The method of claim 40 , wherein the melting point suppressant is boron.
 43. The method of claim 42 , which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 44. The method of claim 43 , wherein the High Velocity Oxygen Fuel process utilizes a Diamond Jet 2600 spray gun.
 45. The method of claim 44 , wherein the spray gun utilizes a powder feed rate of about 5 pounds per hour.
 46. The method of claim 32 , wherein said flame spraying utilizes a fuel rich flame.
 47. The method of claim 46 , wherein said flame spraying is a High Velocity Oxygen Fuel process, and wherein said spraying preplaces the powder braze alloy on the surface.
 48. The method of claim 47 , wherein the High Velocity Oxygen Fuel process utilizes H₂ as its fuel.
 49. The method of claim 48 , wherein the velocity of the powder is about 1,200 ft./sec. to 1,600 ft./sec.
 50. The method of claim 49 , wherein the carrier gas is N₂.
 51. The method of claim 49 , wherein the spray distance is about 9 inches.
 52. The method of claim 51 , which further includes the steps of roughening and degreasing the surface.
 53. The method of claim 51 , wherein the braze alloy is a nickel super alloy.
 54. The method of claim 51 , wherein the melting point suppressant is boron.
 55. The method of claim 53 , wherein the melting point suppressant is boron.
 56. The method of claim 55 , which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 57. The method of claim 56 , wherein the High Velocity Oxygen Fuel process utilizes a Diamond Jet 2600 spray gun.
 58. The method of claim 57 , wherein the spray gun utilizes a powder feed rate of about 5 pounds per hour.
 59. The method of claim 32 , wherein: said flame spraying is a High Velocity Oxygen Fuel process utilizing H₂ as a fuel; said flame spraying utilizes a neutral flame; said flame spraying preplaces the braze alloy on the surface; said providing includes a nickel super alloy as the braze alloy; and which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit.
 60. The method of claim 32 , wherein: said flame spraying is a High Velocity Oxygen Fuel process utilizing H₂ as a fuel; said flame spraying utilizes a fuel rich flame; said flame spraying preplaces the braze alloy on the surface; said providing includes a nickel super alloy as the braze alloy; and which further comprises preheating the surface to a temperature of at least 150 degrees Fahrenheit. 